Fusible electric protective device



Oct. 27, 1942. M. B. woon FUsIBLE ELECTRIC PROTECTIVE DEVICE Filed June l1, 1940 fzvenor,

Patented ct. 27, 19,42

z,aoa,14z Y EUsIIILE ELECTRIC PROTECTIVE DEVICE Morris B. Wood, Newbury, Mass., assigner to The Chase-Shawmut Company, Newburyport, Mass., a corporation of Massachusetts Application June 11, 1940, Serial No. 339,882

19 Claims. (Cl. 20o- 123) This invention relates to electric circuit protective devices and especially to thermal cutouts or fusible protective devices characterized by the use Aof a low melting temperature metal for releasably connecting together the separable current conducting elements of the device, said current conducting elements including means for melting the low melting temperature metal to eiiect the release of one of the conducting elements from another to interrupt the circuit.

One of the objects of the present invention is to provide an improved thermal cut-out or fusible protective device wherein a pair of fusible conductors are electrically and mechanically connected by a mass of readily fusible metal in such a manner that the fusible metal will become fused to permit separation of the parts after the cut-out or protective device has been subjected to a moderate overload for a predetermined period of time. As illustrated herein, this object is attained by the use of a`pair of substantially identical fuse links having end portions which are cupped and which are arranged to be connected together by a low melting temperature metal and which upon melting or fusing of the low melting temperature metal are arranged to be separated by spring means and especially by a spiral spring which is located within the cupped portions of the fuse links and under tension to separate the ends thereof.

Another object of the present invention is to provide a simple effective device of the type above referred to which is capable of being readily and economically manufactured in quantity and under conditions which provide for substantially identical performance of devices intended to have the same current ratings.

\ independently of the metal mass when traversed A further objectof the invention is to provide 7 ciently heated by being traversed by a moderate overload for a suitable period of time and permit spring means to effect the rapid and wide separation of the released parts to effect the interby a heavy overload to effect the more rapid in-` terruption of such heavy overload current.

A still further object of the invention is generally to improve the Construction and operation of thermal cut-outs or fusible protective devices.

With the above and other objects and features in view, the invention 'will now be described with reference to the accompanying drawing in which:

Fig'. 1 is a view in cross-section illustrating a preferred embodiment of the present invention;

Fig. 2 is a plan view illustrating the fusible conducting element of the present invention;

Fig. 3 is a view in section similar to Fig. 1 but illustrating the 'position of the parts after the low melting temperature metal has been fused by a low overload current;

Fig. 4 is a view similar to Fig. 3 but showing the parts after circuit interruption;

y Fig. 5 is a view in section illustrating, on a somewhat enlarged scale, a still further embodiment of the present invention.

The fusible protective device embodying the present invention chosen for the purposes of illustration is of the cartridge type and includes a cylindrical body I0 formed of vulcanized fibre or other suitable insulating material. The fuse body I0 is open at both ends and provides an internal chamber I2. The ends of the body I0 are closed by discs Il having slotted diametrical openings I6 therethrough. The discs I4 are maintained in position on the ends of the fuse body Il byvmetal end caps or ferrules I8 which are internally threaded and which are screwthreaded onto the ends of the casing. With the construction illustrated the end caps constitute the terminals of the fuse. The discs Il and the screwcaps I8 preferably are formed of brass but it is evident that they may be formed of any other suitable electrical conducting material.

The slotted openings I6 in the discs I4 are arranged removably to receive the end portions of a cut-out or fuse member 20 which, as clearly illustrated in Figs. 1, 3 and 4, are inserted through the openings I6 and bent over on the outside of the discs Il so that the ends of the cut-out or fuse member 20 are securely clamped between the discs I4 and the end walls 2l of the caps I8.

This construction above described is wellknown in the prior art and illustrates one form of so-called renewable fuse. It is evident, howi ruption of the current flow, the parts also ,havever, that, if desired, a different end cap construction could be used for removably securing the fusing or cut-out element within the cap or the ends of the fuse element 20 could extend through openings formed in the end caps and secured in position by any suitable means, such for example as solder, thus forming a one-time fuse instead of a renewable fuse such as illustrated herein. For the purposes of the present invention the construction of the terminal structure of the fuse and the manner of securing the fusible element 20 to the terminals is not important and any suitable known arrangement may be employed.

As illustrated most clearly in Fig. 2, the fusible element 2|! is formed preferably of two substantially identical fuse links 22 formed for example, of copper, zinc, or other suitable fuse link material, each having a fusing portion 2l. The fuse links 22 need not, however, be identical but may have different current carrying characteristics. For example, one element or link may be designed to fuse at relatively low currents while the other link may be designed to fuse at a substantially higher current. Thus, one of the elements will act as a fuse link while the other will act as a heating conductor. The overlying or contiguous ends of the fuse links 22 each have a portion thereof formed, as illustrated, into a cup shaped portion 26. The open ends of these cup-shaped portions face each other to permit a compression spring 2l to be placed within the cup shaped portions 26. The overlying ends of the fuse links 22 are scured together by low melting temperature solder 30 having a melting temperature that is less than 'that of the link material and is l'ocated in approximately the middley of the fusible element and midway between the terminal end caps.

The low melting temperature solder softens or fuses when the cartridge fuse is subjected to moderate overload currents for a predetermined period of time. 'I'he fuse links 22 have an electrical resistance high enoughto generate sumcient heat to melt the low melting temperature solder I when the device has been subjected to a moderate overload for a predetermined period of time. When the low melting temperature solder 30 becomes fused or softened sufficiently to release its hold on the overlapped link-ends,

the compression spring 2l contained within the cupped end portions 2l forces the ends of the overlapping links 22 apart. Y

This separating operation causes the entire current to be carried by the compression spring 2l which, as illustrated, is formed of very small diameter high resistance wire and which blows or fuses practically instantly, thus interrupting the electrical circuit through the device. The circuit interrupting arc consumes also the cupped ends of the links so that the circuit is nally interrupted by the insulating gap interposed between the links. If the ends of the links are not consumed with or before the spring, the ends may re-engage after the spring has fused. The re-engagement, however, is a high resistance contact which causes the immediate fusing of the contacting parts and the interruption of the circuit.

'Ihe fusing of the spring 2l is, for the purposes of the present invention, merely incidental to the interruption of the circuit caused by the separation of the link ends, it being more convenient to allow the spring to fuse than to provide a non-conducting resilient in the place of the metal spring.

Ii', however, it is, for some 75 purposes, desirable to employ a conducting spring and to prevent the spring from fusing by conduction of the circuit current through it following the separation of the link ends this can be done as illustrated in Fig. 5. As illustrated in this figure, one or both of the overlapping fuse end portions may be provided with a cup 22 which is formed of insulating material, such, for example, as porcelain, bre or any other suitable material which is not adversely aected by the circuit interruptlng arcor the heat of the fuse links to impair the performance of the fuse. The insulating cup 32 is supported in an opening formed in one end portion of one of the fuse links, and thus insulates one end of the metal compression spring 34 from the fuse link 22 with which it is associated. 'I'he other fuse link 22 has a cuplike portion 20 which is substantially identical with the ones illustrated in Figs. l to 4, inclusive. Thus, when the device embodying the modification illustrated in Fig. 5 is subjected to a moderate overload for a predetermined period of time the low melting temperature solder 30 will fuse, thus separating the overlapping ends of the fuse links 22 in the same manner as illustrated in Fig. 3 but since one end of the spring 34 is insulated from onel of the links 22 the spring will carry no current.

When the fusible element ls overload currents the fusing necks 24 fuse practically instantly and effect the interruption of the circuit before the readily fusible metal 3l has had time to be heated to the melting'tempertraversed by heavy ature, that portion of the fusible element between the fusing necks dropping out of its normal posiytion and thereby increasing the circuit interruptingV gap as is common with the so-called drop-out type of fusible element.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

l. In a fusible protective device, a pair of conductors, readily fusible means for connecting the adjacent ends of the conductors to each other in overlapping relation, and means interposed between the overlapping ends for tensioning only the overlapping ends and for separating the overlapping ends of the conductor upon fusing of the readily fusible means.

2. In a fusible protective device, a heating conductor, a flexible conductor, readily fusible means for connecting one end of the heating conductor to one end of the flexible conductor in overlapping relation, and means carried by said conductors arranged to tension only the overlapping ends to separate the overlapping ends of the heating conductor and the flexible conductor to interrupt the circuit through the device when said readily fusible means is heated to a fusing temperature.

3. In a fusible protective device, a heating conductor, a flexible conductor, readily fusible means for connecting one end of the heating conductor to one end of the flexible conductor, and means interposed between the connected ends arranged upon fusing of the readily fusible means to forcibly separate the ends to interrupt the circuit.

4. In a fusible protective device, a pair of heating conductors having their end portions arranged in overlapping relation, readily fusible means for connecting the overlapping portions of the heating conductors, and means for tensioning the overlapping portions only of the heating conductors and arranged to interrupt the of the readily fusible means.

6. In a fusible protective device, a heating conductor having a cup shaped portion adjacent to one end thereof, a flexible conductor having a cup shaped portion adjacent to one end thereof, readily fusible means for connecting the end portions of the conductors in overlapping relation with the cup shaped portions overlying each oth'er, and means located within the cup-shaped portions arranged upon fusing of the readily fusible means to separate the overlapping ends of the conductors to interrupt the circuit.

'1. In a fusible protective device, a pair of conductors, each having a 4fusing portion and a cup-shaped portion formed adjacent to one end of each conductor, said cup-shaped members being arranged to overlie eachother with their open ends facing each other, readily fusible means for connecting the end portions of th'e conductor to each other, and spring means located Within the cup-shaped portions of the conductor for tensioning the end portions of the 35 conductors and arranged to interrupt the circuit by separating the overlapped end portions upon fusing of the readily fusible means.

8. In a fusible protective device, a pair of fusible conductors, each having a fusing portion arranged to be fused when traversed by currents approximating a short-circuit in value, said conductors each having a cup-shaped por'- tion formed adjacent to one end thereof, a readily fusible metal for connecting the overlapping ends of the conductors with the cup-shaped portions thereof overlying each other, and a compression spring located. within said cup-shaped portions and arranged upon fusing fof the readily fusible metal to separate the overlapping ends thereof to interrupt the circuit through the device. P

9. In a cartridge fuse, a fuse casing, end terminals on said casing, a fusible conductor connected to one of said terminals, a second conductor connected to th'e other end terminal, readily fusible means for connecting the over` lapping contiguous ends of the conductors, and means carried between said overlapping con'- nected ends for separating the overlapping ends upon fusing of the readily fusible means,

10. In a cartridge fuse,an insulating casing, end terminals on the casing, a pair of fusible conductor members each connected at one end to said terminals, the contiguous overlapping end portions of the conductors having superposed cup-shaped portions, readily fusible means for connecting said contiguous superposed portions together, and spring ineansvin said cupshaped portions maintainedunder tension by said readily fusible means and arranged upon fusing of said readily fusible means to separate the overlapping ends to interrupt the circuit through the cartridge fuse.

11. In a cartridge fuse, end terminals, a pair 75 of fusible conductors connecting said terminals, the contiguous ends of said fusible conductor being overlapped and having superposed cupshaped portions, readily fusible metal for connecting the overlapping ends of the conductor,

I and a compression spring located within said cup-shapedportions and maintained under tension by said readily fusible metal and arranged upon fusing of the readily fusible metal to separate the overlapping ends thereof to interrupt the circuit through the device.

12. A fusible element for an electric fuse, said element comprising a pair of fusible links joined releasably in end to end relatio1i\by a low melting temperature solder arranged t`o`receive from the fuse links heat generated therei`n\by current traversing the links to soften and release its hold on the links, and a spring carried by said ele-r ment as a unitary part thereof exerting pres-y sure in opposite directions on the joined parts' only of said links to bend the links in opposite directions and separate the links when the solder releases its hold on the links. f

13. A fusible element for an electric fuse, said element comprising a pair of fusible links joined releasably in end to end relation by a low melting temperature solder arranged to receive from the fuse links heat generated therein by current traversing the links to soften and release its hold on the links, and a spring carried by said ele'I ment as a unitary part thereof exerting pressure in opposite directions on the joined parts only of said links to bend the links in opposite directions and separate the links when the solder releases its hold on the links, each of said links having a fusing Aneck therein, the necks being lo' cated on opposite sides'of the joined parts of the links and the necks being arranged to fuse more promptly than the solder when traversed -by a sunlciently high current.

14. A fusible element for an electric fuse, said element comprising a pair of fusible links arranged approximately in line with their confronting end parts joined together by a solder which melts at a temperature lower than the melting temperature of the link material and which is arranged to receive from both of the links heat generated therein by current traversing the links, and springs means interposed between the joined ends of the conductors and responsive to the melting of the solder to bend the links in opposite directions out of the line n of the links and separate said end parts.

heat generated therein by current traversing the links, and spring means interposed between the confronting ends of the conductors and responsive to the melting of the solder to bend the links in opposite directions out of the line of the links and separate said end parts, said links having readily fusible necks on opposite sides of the joined end parts permitting the joinedV end parts to drop out of the line of the links upon the fusing of said necks in rel sponse to a sufficiently high current4 which traverses and fuses said necks before it fuses said solder.

16. A fusible element for an electric fuse, said element comprising a pair of fusible links arranged approximately in line with their confronting end parts joined together by a solder which melts at a temperature lower than the melting temperature of the link material and which is arranged to receive from both of the links heat generated therein by current traversing the links, and a metal compression spring interposed between said joined end parts exerting pressure thereon in opposite directions to bend the links and separate the end parts, said spring having its ends in electrical contact with said links and having a high resistance compared with the resistance of said links and arranged to fuse quickly following the separation of said link ends.

17. A fusible element for an electric fuse. said element comprising a pair of fusible links arranged approximately in line with their confronting end parts joined together by a solder which melts at a temperature lower than the melting temperature of the link material and which is arranged to receive from both of the links heat generated therein by current traversing the links, and a metal compression spring interposed between said joined end `parts exerting pressure thereon in opposite directions to bend the links and separate the end parts, said spring having means excluding it from the circuit through said fusible element.`

i8. A fusible element for an electric fuse, said' element comprising a pair of fusible links arranged approximately in line with their confronting end parts Joined together by a solder which melts at a temperature lower than the melting temperature of the link material and which is arranged to receive from both of the links heat generated therein by current traversing the links, and a compression spring interposed between said joined end parts exerting pressure thereon in opposite directions to bend the links and separate the end parts, said spring being excluded from the circuit through the fusible element.

19. A renewable fusible link for electric fuses comprising as a unitary article of manufacture two electric conductors arranged generally in line with overlapped ends joined releasably' together by a readily fusible metal, at least one of said conductors having substantial electrical resistance to generate heat therein when traversed by a suitable current to ultimately soften said fusible metal and cause it to release its bond between said conductors. at least one of said conductors being fusible before the softening of said fusible metal when traversed by a sumciently heavy current that would ultimately soften said fusible metal, at least one of said conductors being flexible to move laterally away from the cooperating conductor when the bond therebetween is removed, and spring means operi ative to separate said conductors laterally when the bond between them vis released. said spring means being carried entirelyl by said fusible link and the end parts of said conductors constituting free unstressed link terminals.

MORRIS B. WOOD. 

